The present invention relates to a molding method for a bicycle metal frame, in which the male and female molds are mated to define a bicycle frame mold cavity which is vacuumized. Then by way of high pressure filling, the clean and pure molten metal is filled into the mold cavity and a spilling back flow tank is defined by the mated male and female molds by way of drawing out the mold core to achieve an integrally molded bicycle frame having a polished surface with complete metal phase and good structural strength. The processing flow of the bicycle frame is simplified and the manufacturing procedure is speeded. Mass-production becomes possible so that the cost is lowered to promote competition.
FIGS. 1 and 2 show the conventional manufacturing flow chart of a bicycle metal frame. First, a large diameter aluminum tube 1, a middle diameter aluminum tube 2 and a small diameter aluminum tube 3 which have different diameters and a certain length are provided. Then the large diameter aluminum tube 1 is cut into several upper tubes 4 with a certain length and a five-way tube 5. The middle diameter aluminum tube 2 is cut into several lower tubes 6 with a certain length and the small diameter aluminum tube 3 is cut into several front tubes 7 with a certain length and seat tube 8. Then the upper tube 4 by way of punching and pressing is processed into a long and flat elliptic shape and two end faces thereof are cut into longitudinal concave end faces 4'. One end face of the lower tube 6 is cut into longitudinal concave end face 6', while the other end face thereof is cut into transverse concave end face 6". Finally, a flat upper tube 4, a five-way tube 5, a lower tube 6, a front tube 7 and a seat tube 8 are provided. One longitudinal concave end face 4' of the upper tube 4 is welded at an upper section of the front tube 7, while the other longitudinal concave end face 4' is welded at a certain position of the seat tube 8. Then the longitudinal concave end face 6' of the lower tube 6 is welded at a lower section of the front tube 7, while the transverse concave end face 6" is welded at the center of the outer surface of the five-way tube 5. Then the projecting welding sections are ground and planed to achieve a bicycle frame 9.
The above manufacturing method has some shortcomings as follows:
1. Different diameters of aluminum tubes with different diameters are selected and processed. This complicates the selection of material. PA1 2. The selected different diameters of aluminum tubes are first according to specifications respectively cut into different lengths of upper tubes 4, five-way tube 5, lower tubes 6, front tube 7 and seat tube 8. The upper tube 4 by way of punching and pressing is further processed into long and flat elliptic shape and two end faces thereof are cut into longitudinal concave end faces 4'. One end face of the lower tube 6 is cut into longitudinal concave end face 6', while the other end face thereof is cut into transverse concave end face 6". This complicates the processing operation. PA1 3. The upper tubes 4, five-way tube 5, lower tubes 6, front tube 7 and seat tube 8 are welded together by a specialist. However, the welding can achieve a limited connection strength so that the safety can hardly be ensured. Moreover, the projecting welding sections must be further processed and planed. This may detract from the appearance of the frame. PA1 4. The manufacturing procedure of the bicycle frame is time-consuming and laborious. This increases the manufacturing cost and makes it impossible to mass-produce the bicycle frame and promote competition on the market.